Heat exchanger and method of performing chemical processes

ABSTRACT

A housing for a heat exchange apparatus including a fluid passageway partially defined by a baffle plate having an extended portion. The heat exchange apparatus further includes an array of fluid conduits extending through the fluid passageway. The housing includes a plurality of housing members each having a wall and at least one flange extending from the wall. The flanges of adjacent housing members are joined at a flange joint, and the flange joint is configured to fixedly receive the extended portion of the baffle plate. The apparatus also includes a plate member is provided within the fluid passageway and intumescent material fills a gap between the baffle plate and the plate member. Additionally, a second baffle plate is provided that defines a portion of a second fluid passageway, where a refractory gasket and a layer of intumescent material are provided between the first and second baffle plates.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to heat exchange devices and methods of performing chemical processes using heat exchangers.

[0003] 2. Discussion of the Background

[0004] Chemical processing systems combining heat exchangers and catalytic reactors are well-known in the art. Significant progress has been made in the field of single assemblies that combine heat exchange and reaction functions due to an increased sensitivity to mechanical equipment size and cost. An example of this trend is the advanced hydrogen generating reactor disclosed in U.S. Pat. No. 6,497,856 to Lomax et al., which combines several heat exchangers and reactors into a single mechanical device. Such combined reactors have been advantageously applied to hydrogen generation for fuel cells, although many other applications are possible.

[0005] In most catalytic reactors, reaction rates are extremely sensitive to temperature. In some reactions, the actual product distribution and reaction route can also be profoundly affected by small swings in temperature. One problem encountered whenever a large heat exchange array is integrated with a large adiabatic reactor, such as a packed bed or monolithic reactor, is the presence of temperature gradients across the catalyst bed. These temperature gradients necessarily arise in any cross-flow heat exchange structure, such as a baffled tubular heat exchanger or a plate-fin heat exchanger. In traditional systems using separate heat exchangers and reactors, the fluids of different temperatures would be mixed after heat exchange and before being piped to the subsequent reactor. Accordingly, traditional systems did not encounter concerns regarding temperature gradients. However, these systems required more complicated, less compact, heavier equipment with high heat losses as compared to an integrated reactor and heat exchanger.

[0006] Referring to FIG. 4, the reactor of the Lomax et al. patent has an inlet for mixed, pre-vaporized fuel and steam 101, which communicates with a plenum 102, which distributes the mixture to the array of reactor tubes 103. The reactor tubes 103 are provided, as is illustrated in the cut-away portion of FIG. 4, with a charge of steam reforming catalyst material 105. This catalyst material 105 may be a loose packing as illustrated, or may be a catalytic coating, or may be a section of monolithically-supported catalyst. Such coated, packed bed, or monolithic catalyst systems are well known to those skilled in the art. The reactor tubes are also provided with a water gas shift catalyst 150, which is located downstream from the steam reforming catalyst 105. The tubes 103 communicate with an outlet plenum 107, which delivers the reformate product to an outlet port 108. The reactor tubes 103 pass through holes in one or more baffles 109. The baffles 109 are chorded to allow fluid to flow around the end of the baffle and along the tube axis through a percentage of the cross-sectional area of the shell. The direction of the chorded side alternates by one hundred and eighty degrees such that fluid is forced to flow substantially perpendicular to the long axis of the tubes 103.

[0007] The reactor has a cold air inlet 112 in a shell-side of a water gas shift section, as well as, a hot air outlet 113. Most of the shell-side air is prevented from bypassing the hot air outlet 113 by an unchorded baffle 114, which fits snugly against the shell assembly 110 inner wall. The reactor is further provided in the shell side of a steam reforming section with a hot combustion product inlet 115 and a cooled combustion product outlet 116. The reactor is also provided with an external burner assembly 118. An adiabatic water gas shift reactor 121 is appended to the outlet tube header 106. The reactor employs both baffles 109, as well as, extended heat exchange surfaces, such as a plurality of closely-spaced plate fins 120, on the outer walls of the reactor tubes 103. The fins 120 are attached to all of the reactor tubes 103 in the tube array.

[0008] It has been determined that in the example of catalytic water gas shift as taught in the patent to Lomax et al., at temperatures below 350° C. the reaction rate is very slow, while at temperatures above 400° C. the thermodynamically-limited extent of reaction is undesirably low. Worse yet, at temperatures above 450° C. an undesirable side reaction to create methane begins to occur at appreciable rates. Thus, the total preferred operating temperature gradient is less than 50° C., and a gradient above 100° C. is quite undesirable. In the patent to Lomax et al., the feed gas to the catalytic water gas shift reactor is cooled with air that is near room temperature. The cold air used for cooling can cause extremely low temperatures in the zones of the catalytic reactor adjacent to the air inlet. Experience has shown that local temperature gradients of over 200° C. routinely occur, thus causing a significant reduction in reactor performance.

SUMMARY OF THE INVENTION

[0009] In an effort to eliminate these disadvantages in the systems described above, the inventor has provided an improved apparatus combining a heat exchanger with a subsequent chemical reactor in order to control thermal gradients in the chemical reactor.

[0010] The present invention further advantageously provides a method of performing chemical processes using heat exchangers that are configured to control thermal gradients. For example, the present invention provides a method of performing chemical processes using heat exchange arrays that are configured to minimize thermal gradients and that are combined with chemical reactors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A more complete appreciation of the invention and many of the attendant advantages thereof will become readily apparent with reference to the following detailed description, particularly when considered in conjunction with the accompanying drawings, in which:

[0012]FIG. 1 is a perspective view of a heat exchanger with a tailored heat transfer matrix of the present invention with an outer housing and an appended chemical reactor removed for clarity;

[0013]FIG. 2 is a perspective view of the heat exchanger of FIG. 1 with a chemical reactor attached thereto;

[0014]FIG. 3 is a side view of the heat exchanger with a tailored heat transfer matrix of FIG. 1 with an outer housing and an appended chemical reactor removed for clarity; and

[0015]FIG. 4 is a reactor of the Lomax et al. patent with plate fin heat exchange surfaces attached to the tubes on the shell side and an adiabatic water gas shift reactor zone placed after the convectively cooled water gas shift reactor zone.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. In the following description, the constituent elements having substantially the same function and arrangement are denoted by the same reference numerals, and repetitive descriptions will be made only when necessary.

[0017]FIGS. 1-3 depict a heat exchange array 1, which can be used, for example, in a catalytic water gas shift reactor portion of the reactor as taught in the patent to Lomax et al. The heat exchange array 1 includes an array of conduits 3, which are preferably parallel tubes however conduits of various shapes, sizes, and configurations, and conduits of differing shapes and sizes can be used. Although a tubular heat exchange array is shown in FIGS. 1-3, other types of heat exchange arrays may be employed such as plate fin where elongated, essentially-planar fluid passages are formed with attached layers of heat exchange fins. FIGS. 1-2 are depicted with an outer shell assembly or housing 10 (see FIG. 3) removed in order to reveal the array of tubes 3.

[0018] The array of tubes 3 depicted in FIGS. 1-3 includes a plurality of rows of tubes. A row includes two or more aligned tubes. FIG. 3 depicts a side view of the array of tubes 3, which includes ten rows of tubes 3 a-3 j. The first row of tubes 3 a is positioned at a location closest to an inlet 12 in a shell-side of a water gas shift section of the reactor as compared to the remaining rows of tubes 3 b-3 j. A first fluid flows from the inlet 12 and, due to the configuration of the baffle plate 9, travels along a flow path in the direction indicated by arrow A and weaves through the array of tubes 3 around outer surfaces of the tubes. Based on the flow of the first fluid, the first row of tubes 3 a is upstream of the second row of tubes 3 b, which is upstream of the third row of tubes, which is upstream of the fourth row of tubes 3 d, etc.

[0019] A second fluid flows from a common plenum into the tubes 3. The reactor tubes 3 are provided with a water gas shift catalyst bed 50 in the catalytic water gas shift reactor portion of the reactor. The portion of the reactor tubes 3 in the catalytic water gas shift reactor portion form a flow path for the second fluid. The second fluid flows downward as indicated by arrow B in FIG. 3 and exits through tube ends 3 into an attached chemical reactor, such as an adiabatic water gas shift reactor 21, which includes a bed of water gas shift catalyst and is appended to an outlet tube header 6 as depicted in FIG. 2.

[0020] The first fluid exchanges heat with the second fluid, which flows substantially perpendicular to the first fluid. The second fluid may heat or cool the first fluid depending upon the configuration of the reactor. The array of tubes 3 is provided with external heat exchange fins 20, which can enhance heat transfer between the first fluid and the second fluid. The fins 20 may be bonded to the reactor tube by brazing, or more preferably by hydraulically expanding the tubes 3 into close contact with the plate fins 20 such that a thermally conductive joint is formed between the fins 20 and the tubes 3 that are in contact therewith.

[0021] A finned tubular heat exchanger with rectangular plate fins 20 is shown in FIGS. 1-3, but the practice of the present invention may be easily extended to other fin geometries and types. Further, the fins in the tubular array need not be planar fins (or plate fins) as shown in FIGS. 1-3, but may be individually attached fins (e.g., a series of circular fins attached at intervals along the length of an individual tube), or continuously-applied helical fins, or any other type of heat exchange fin apparent to one skilled in the art. The fins can extend out from a given tube or row of tubes and not be attached to the other rows, thereby not providing thermal conduction between the fin and several rows of tubes.

[0022] The present invention advantageously minimizes a temperature differential between a maximum temperature of a fluid in the second flow path (i.e., in any one of the tubes in the array of tubes 3) and a minimum temperature of the fluid in the second flow path by providing tubes in the array of tubes 3 with different predetermined amounts of total heat exchange surface area per unit volume, where the predetermined amounts are dependent upon a location distance of a tube to an inlet 12 of the first flow path indicated by arrow A. The amount of total heat exchange surface area of a given tube can be identified by the total number and size of plate fins that are connected in a thermally conductive manner to that tube, and adding up all of the surface area of the tube and the respective thermally connected fins that are exposed to the first fluid. The total heat exchange surface area is then determined per unit volume of the tube in question, which represents the volume of second fluid provided within the tube in question at any given time. The present invention advantageously varies the amount of heat exchange area per unit volume gradually from the first fluid inlet 12 towards a first fluid outlet such that the rate of heat exchange within the catalytic water gas shift reactor portion of the reactor can be controlled to limit excursions from a desired second fluid outlet temperature.

[0023] In the embodiment depicted in FIGS. 1-3, the plate fins 20 are sized so that tubes in row 3 a, which is nearest to the inlet 12 of the first fluid (i.e. furthest upstream in the first fluid flow path), are connected in a thermally conductive manner to fewer fins per unit length than the tubes in the next nearest row 3 b. In turn, the tubes in row 3 b are connected in a thermally conductive manner to fewer fins per unit length than the next nearest row 3 c. The tubes in rows 3 d-3 j are connected in a thermally conductive manner to all of the fins 20, thereby achieving the highest thermal conductivity per unit length of tube.

[0024] In the embodiment depicted in FIGS. 1-3, five sets of plate fins 20 are provided in a stacked arrangement. Each set of plate fins 20 includes a first plate fin 20 a that is connected in a thermally conductive manner to all of the tubes in rows 3 a-3 j, a second plate fin 20 b that is connected in a thermally conductive manner to all of the tubes in rows 3 b-3 j, a third plate fin 20 c that is connected in a thermally conductive manner to all of the tubes in rows 3 c-3 j, and a fourth plate fin 20 d that is connected in a thermally conductive manner to all of the tubes in rows 3 d-3 j. Thus, each tube in row 3 a is connected to five fin plates along the length of tube that extends through the first fluid flow path, each tube in row 3 b is connected to ten fin plates along the length of tube that extends through the first fluid flow path, each tube in row 3 c is connected to fifteen fin plates along the length of tube that extends through the first fluid flow path, and each tube in rows 3 d-3 j is connected to twenty fin plates along the length of tube that extends through the first fluid flow path. Many different variations of the configuration of fin plates depicted in FIGS. 1-3 are possible, as will be readily apparent to one of ordinary skill in the art in light of the disclosure set forth herein. For example, a larger or smaller number of rows can be provided, a larger or smaller number of fins can be provided in the first fluid flow path, a larger or smaller number of sets of fins can be provided or a different configuration of fin lengths can be provided such that the fins are in a different pattern than shown or are not in any particular pattern, and the fins can be configured to have different sizes than those shown whereby the number of fins per unit length is different only for row 3 a, or is different for each of rows 3 a-3 j, or any configuration in between.

[0025] By providing less heat exchange area per unit heat exchange volume of tube and/or less heat exchange area per unit length of tube in the rows of tubes nearest the incoming first fluid, the rate of heat exchange between the first and second fluids may be advantageously reduced relative to that obtained in a related-art configuration where all of the heat exchange matrix would possess the same heat exchange area per unit volume. By varying the amount of heat exchange area per unit volume gradually from the inlet 12 of the first fluid towards the outlet of the first fluid, the rate of heat exchange may everywhere be controlled to limit excursions from the desired second fluid outlet temperature. This method has the disadvantage of reducing the overall performance of the heat exchanger relative to related art configurations with constant heat transfer matrix properties, but advantageously provides almost complete control over the temperature gradient at the second fluid passage outlet 4. This advantage can be achieved without provision of any mixing dead volume, or any fluid mixing means such as a static turbulator or a motor-actuated mixer. All of these mixing devices result in a system larger in volume, higher in complexity, and, with the actuated system, lower in reliability than achieved in the present invention.

[0026]FIGS. 1-3 depict a particularly-preferred embodiment where plate fins 20 having a varying number of rows are placed around an array of tubes 3 in a repeating pattern. This embodiment is readily assembled as the fins 20 may be provided with self-spacing collars. FIG. 1 shows the plate fins spaced widely apart for clarity, with their extended collars not in contact. In a more preferred embodiment the fin collars are in contact between each fin, thus providing uniform spacing of the fins and thus uniform fluid flow. A repeating pattern of fins 20 also provides advantageously uniform fluid flow across the entire area of the first fluid flow path. Other preferred embodiments achieve a similar flow distribution by installing evenly spaced individual fins, but with much higher assembly difficult, or by installing continually-finned tube with a different fin spacing for each row. For plate-fin heat exchange matrices, the same effect may be achieved by installing strips of fin of varying fins per inch or with varying degrees of surface enhancement to achieve the same gradual variation in heat transfer performance.

[0027]FIG. 2 depicts the heat exchange matrix of the present invention with an attached chemical reaction vessel 21. The reaction vessel may have any shape, although a vessel having a round cross section is shown in FIG. 2. The chemical reactor may be catalytic or uncatalyzed, and may be provided with solid catalyst supports, mass transfer media, a catalyst monolith, or any other typical chemical reactor internal structure known in the art. It is a particular advantage of the present invention that no mixing means is required before the chemical reaction zone.

[0028] The apparatus of the present invention may be configured to create either a specified uniform temperature, or to create a preferred non-uniform gradient. This may be accomplished by treating each row of tubes, or differential element of flow in a plate-fin heat transfer matrix, as a separate heat exchanger for design purposes. The amount of heat transfer area per unit volume of heat exchange matrix may be varied to create the preferred temperature gradient using calculations known to those skilled in the art.

[0029] The apparatus of the present invention is especially well-suited to use in reactors integrating catalytic water gas shift with heat exchange. It is especially advantageous in unitary reactors of the type described in the Lomax, et al. patent.

[0030] It should be noted that the exemplary embodiments depicted and described herein set forth the preferred embodiments of the present invention, and are not meant to limit the scope of the claims hereto in any way.

[0031] Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

What is claimed as new and desired to be secured by Letters Patent of the United States is:
 1. A heat exchange apparatus comprising: a housing; a first fluid passageway provided within said housing, said first fluid passageway being defined by an internal surface of said housing and by a baffle plate, said baffle plate having an extended portion that extends beyond said first fluid passageway; and an array of fluid conduits provided within said housing, said array of fluid conduits extending through said first fluid passageway, wherein said housing includes a first housing member having a first wall and a flange extending from said first wall, said housing further including a second housing member having a second wall and a flange extending from said second wall, and wherein said flange of said first housing member and said flange of said second housing member are joined at a flange joint to said extended portion of said baffle plate at opposite sides of said extended portion.
 2. The heat exchange apparatus according to claim 1, wherein said array of fluid conduits extend through said baffle plate.
 3. The heat exchange apparatus according to claim 1, wherein said first wall and said second wall define a portion of said internal surface of said first fluid passageway.
 4. The heat exchange apparatus according to claim 1, wherein said housing comprises a plurality of housing members each having a wall and at least one flange extending from said wall, wherein flanges of adjacent housing members are joined.
 5. The heat exchange apparatus according to claim 1, wherein said flange of said first housing member is detachably joined to said extended portion of said baffle plate.
 6. The heat exchange apparatus according to claim 5, wherein a seal member is provided in between said flange of said first housing member and said extended portion of said baffle plate.
 7. The heat exchange apparatus according to claim 1, wherein said array of fluid conduits having a plurality of heat transfer fins provided on outer surfaces of said fluid conduits, said plurality of heat transfer fins extending within said first fluid passageway.
 8. The heat exchange apparatus according to claim 1, wherein said baffle plate has a portion with a fluid port.
 9. The heat exchange apparatus according to claim 1, wherein said wall of said first housing member has a fluid connection port.
 10. The heat exchange apparatus according to claim 1, wherein said array of fluid conduits extend through said baffle plate, wherein said extended portion of said baffle plate extends around an entire perimeter of said baffle plate, and wherein said heat exchange apparatus further comprises a second fluid passageway provided within said housing, said second fluid passageway being defined by an additional internal surface of said housing, said array of fluid conduits extending through said second fluid passageway.
 11. The heat exchange apparatus according to claim 10, further comprising: a plate member provided within said first fluid passageway, said array of fluid conduits extending through said plate member, said plate member being mounted to outer surfaces of said array of fluid conduits at a predetermined distance from said baffle plate; and at least one layer of intumescent material provided between said baffle plate and said plate member, said array of fluid conduits extending through said at least one layer of intumescent material, wherein said at least one layer of intumescent material substantially entirely fills a gap between said baffle plate and said plate member.
 12. The heat exchange apparatus according to claim 11, wherein said at least one layer of intumescent material is made of a material that expands at a temperature above about 300° C.
 13. The heat exchange apparatus according to claim 10, wherein said second fluid passageway is further defined by an additional baffle plate having an extended portion that extends beyond said second fluid passageway, said array of fluid conduits extending through said additional baffle plate, said extended portion of said additional baffle plate extending around an entire perimeter of said additional baffle plate, wherein said housing includes a third housing member having a third wall and a flange extending from said third wall, wherein said flange of said second housing member and said flange of said third housing member are joined to said extended portion of said additional baffle plate at opposite sides of said extended portion, and wherein said heat exchange apparatus further comprises: a refractory gasket provided between said baffle plate and said additional baffle plate, said array of fluid conduits extending through said refractory gasket; and a layer of intumescent material provided between said baffle plate and said additional baffle plate, said array of fluid conduits extending through said layer of intumescent material.
 14. The heat exchange apparatus according to claim 13, wherein said refractory gasket and said layer of intumescent material substantially entirely fill a gap between said baffle plate and said additional baffle plate.
 15. The heat exchange apparatus according to claim 13, wherein said layer of intumescent material is made of a material that expands at a temperature above about 300° C.
 16. The heat exchange apparatus according to claim 1, wherein said flange joint comprises expansion means for allowing a distance between said first wall and said second wall to expand under predetermined conditions.
 17. The heat exchange apparatus according to claim 16, wherein said expansion means allows for expansion of the distance in a direction parallel to an axial direction of a fluid conduit of said array of fluid conduits.
 18. The heat exchange apparatus according to claim 16, wherein said expansion means allows for expansion of the distance in a direction perpendicular to an axial direction of a fluid conduit of said array of fluid conduits.
 19. A housing for a heat exchange apparatus including a fluid passageway partially defined by a baffle plate, the baffle plate having an extended portion, the heat exchange apparatus further including an array of fluid conduits extending through the fluid passageway, said housing comprising: a plurality of housing members each having a wall and at least one flange extending from said wall, wherein flanges of adjacent housing members are joined at a flange joint, wherein said flange joint is configured to fixedly receive the extended portion of the baffle plate.
 20. The housing according to claim 19, wherein said housing comprises a first section having a four-sided cross-section including two opposing first housing members and two opposing second housing members, wherein each first housing member has a wall and at least two flanges on opposite sides of said wall, said at least two flanges extending from said wall of said first housing members at an angle of substantially ninety degrees from said wall, wherein each second housing member has a wall and at least two flanges on opposite sides of said wall, said at least two flanges extending from said wall of said second housing members along a plane substantially parallel to said wall, and wherein each flange of said at least two flanges of each first housing member is joined to a flange of said at least two flanges of an adjacent second housing member.
 21. The housing according to claim 20, wherein said housing comprises a second section having a four-sided cross-section including two opposing first housing members and two opposing second housing members, and wherein said second section is stacked upon said first section and joined to said first section.
 22. The housing according to claim 21, wherein said first section has a cross-sectional area that differs from a cross-sectional area of said second section.
 23. The housing according to claim 21, wherein each of said first housing members and said second housing members of said first section have an expansion flange extending from said wall thereof at an angle of substantially ninety degrees from said wall thereof, wherein each of said first housing members and said second housing members of said second section have an expansion flange extending from said wall thereof at an angle of substantially ninety degrees from said wall thereof, and wherein said expansion flanges of said first section are joined to respective expansion flanges of said second section to form four expansion joints between said first section and said second section.
 24. The housing according to claim 23, wherein three of said four expansion joints are configured to fixedly receive extended portions of the baffle plate.
 25. The housing according to claim 23, wherein said expansion flanges of said first section are detachably joined to said respective expansion flanges of said second section.
 26. The housing according to claim 25, wherein a seal member is provided in between said expansion flanges of said first section and said respective expansion flanges of said second section.
 27. The housing according to claim 19, wherein said flange joint comprises expansion means for allowing a distance between said walls of said adjacent housing members to expand under predetermined conditions.
 28. The housing according to claim 27, wherein said expansion means allows for expansion of the distance in a direction parallel to an axial direction of a fluid conduit of said array of fluid conduits.
 29. The housing according to claim 27, wherein said expansion means allows for expansion of the distance in a direction perpendicular to an axial direction of a fluid conduit of said array of fluid conduits.
 30. The housing according to claim 19, wherein said wall of at least one of said plurality of housing members has a fluid connection port.
 31. A heat exchange apparatus comprising: a housing; a first fluid passageway provided within said housing; a second fluid passageway provided within said housing; a baffle plate substantially separating said first fluid passageway from said second fluid passageway; an array of fluid conduits provided within said housing, said array of fluid conduits extending through said first fluid passageway, said baffle plate, and said second passageway; a plate member provided within said first fluid passageway, said array of fluid conduits extending through said plate member, said plate member being mounted to outer surfaces of said array of fluid conduits at a predetermined distance from said baffle plate; and at least one layer of intumescent material provided between said baffle plate and said plate member, said array of fluid conduits extending through said at least one layer of intumescent material, wherein said at least one layer of intumescent material substantially entirely fills a gap between said baffle plate and said plate member.
 32. The heat exchange apparatus according to claim 31, wherein said at least one layer of intumescent material is made of a material that expands at a temperature above about 300° C.
 33. The heat exchange apparatus according to claim 31, wherein said at least one layer of imtumescent material is made of vermiculite.
 34. The heat exchange apparatus according to claim 33, wherein said at least one layer of intumescent material is further made of refractory fibers and a binder.
 35. A heat exchange apparatus comprising: a housing; a first fluid passageway provided within said housing; a second fluid passageway provided within said housing; an array of fluid conduits provided within said housing, said array of fluid conduits extending through said first fluid passageway and said second passageway; and a sealing zone substantially separating said first fluid passageway from said second fluid passageway, said sealing zone comprising: a first baffle plate that defines a portion of said first fluid passageway, said array of fluid conduits extending through said first baffle plate; a second baffle plate that defines a portion of said second fluid passageway, said array of fluid conduits extending through said second baffle plate; a refractory gasket provided between said first baffle plate and said second baffle plate, said array of fluid conduits extending through said refractory gasket; and a layer of intumescent material provided between said first baffle plate and said second baffle plate, said array of fluid conduits extending through said layer of intumescent material.
 36. The heat exchange apparatus according to claim 35, wherein said refractory gasket and said layer of intumescent material substantially entirely fill a gap between said first baffle plate and said second baffle plate.
 37. The heat exchange apparatus according to claim 35, wherein said layer of intumescent material is made of a material that expands at a temperature above about 300° C.
 38. The heat exchange apparatus according to claim 35, wherein said layer of intumescent material is made of vermiculite.
 39. The heat exchange apparatus according to claim 38, wherein said layer of intumescent material is further made of refractory fibers and a binder.
 40. The heat exchange apparatus according to claim 35, further comprising: a plate member provided within said first fluid passageway, said array of fluid conduits extending through said plate member, said plate member being mounted to outer surfaces of said array of fluid conduits at a predetermined distance from said first baffle plate; and at least one layer of intumescent material provided between said first baffle plate and said plate member, said array of fluid conduits extending through said at least one layer of intumescent material, wherein said at least one layer of intumescent material substantially entirely fills a gap between said first baffle plate and said plate member.
 41. The heat exchange apparatus according to claim 40, wherein said at least one layer of intumescent material is made of a material that expands at a temperature above about 300° C.
 42. A method of constructing a heat exchange apparatus including a fluid passageway partially defined by a baffle plate, where the baffle plate has an extended portion, the heat exchange apparatus further including an array of fluid conduits extending through the fluid passageway, said method of constructing comprising the steps of: providing a plurality of housing members each having a wall and at least one flange extending from the wall; joining flanges of adjacent housing members at a flange joint, wherein the flange joint fixedly receives the extended portion of the baffle plate, and wherein a final housing member is not joined in this step; inserting the array of fluid conduits in fluid passageway; providing a plurality of heat transfer fins on outer surfaces of the fluid conduits of the array of conduits; and joining flanges of the final housing member to adjacent housing members to form a closed housing. 